INTERACTION OF SNOW BLIGHT, PHACIDIUM INFESTANS, AND PINUS SYLVESTRIS IS AFFECTED BY SURROUNDING VEGETATION
Å HAGNER and L ERICSON
Dept of Ecological Botany, University of Umeå, S-901 87 Umeå, Sweden
Background and objectives
Boreal forests are characterised by ericaceous plant species dominating the field layer while mosses and lichens form a closed bottom layer. Ericaceous dwarf shrubs have a documented capacity of inhibiting seed germination and seedling establishment among conifers. This may affect tree regeneration in late successional stages.
The snow blight pathogen Phacidium infestans attacks pine needles during winters by means of mycelial growth through snow. The spread of the disease may be affected by the presence of different ericaceous dwarf shrubs  and in a natural regenerated pine stand, infested with snow blight, pine survival in was strongly associated with Calluna vulgaris over a period of 4 years .
Materials and methods
In field experiments during the winters of 1994-95 and 1995-96 we tested if the spread of Ph. infestans on and among host plants, differed in relation to surrounding vegetation (i.e. Calluna vulgaris, Vaccinium vitis-idaea and lichens Cladina spp.).
Results and conclusions
Over the two winters snow conditions differed considerably, which also affected the amount of disease caused by Ph. infestans . Still the spread of snow blight by mycelial growth was clearly inhibited by the tested field-layer species. Pines were least diseased if placed inside a patch of vegetation and most diseased when placed on lichens. The results indicates that it might be beneficial for young pine plants to be growing in ericaceous vegetation where they may escape attack by snow blight.
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